In cardiac surgery, the heart is often deprived of blood for a period of time. When this occurs, the heart's energy requirements must be reduced to prevent heart damage. In the prior art two methods are generally used to accomplish this metabolism reduction or myocardial preservation.
One prior art method consists of an initial infusion of a cardioplegic solution into the coronary arteries followed by continued low-flow infusion or intermittent higher-flow infusion. The first infusion initially cools and arrests the heart while the subsequent low-flow infusion or higher-flow infusion maintains the low temperature. The major drawback of this method is that the cardioplegic solution enters the patient's bloodstream thereby diluting the blood with a drug that tends to stop heart action.
Another prior art method, which is sometimes combined with the previously described one, is an external lavage of the heart with cold normal saline. The major drawback of the topical lavage is that the saline pored over the heart becomes mixed with blood in the patient's chest cavity thereby diluting it. Further, the lavage also has an undesirable tendency to cool the surgeon's fingers.
It is also known that organs can be cooled or heated by placing a pad near them, and passing hot or cold fluid through the pad. Shioshvili U.S. Pat. No. 3,738,372 shows an elastic cooling pad which conforms to a kidney and is used to cool it when it is cut off from blood supply. The pad walls, however, are only separated by the fluid in the pad which is under positive pressure. Miley U.S. Pat. No. 3,888,259 shows a standard hypothermia pad which is designed to wrap or otherwise contact a patient. This pad is connected by a return line to a fluid pump, but it does not conform to the patient's body because of negative pressure. Further, fluid only flows through tubing in the pad, the walls of which are not otherwise separated.